High voltage switching output drivers are used for many electronic applications. For example, high voltage switching output drivers are used in high voltage output stages, class D amplifiers, direct current to direct current (DC-to-DC) converters, and Power Management Integrated Circuits (PMICs).
A class-D amplifier or switching amplifier is an electronic amplifier where all power devices (typically power transistors) are operated as binary switches. These power transistors are often Metal Oxide Semiconductor Field Effect Transistors (MOSFETs). In operation, the MOSFETs are typically either fully on or fully off. A DC-to-DC converter is an electronic circuit which converts a source of direct current (DC) from one voltage level to another, and are often used in battery powered electronic devices. High voltage switching output drivers can be used in conjunction with the voltage conversion. While a PMIC may more than one function, DC to DC conversion and voltage scaling, both of which can rely upon high voltage switching output drivers, can be employed.
FIG. 1 is a block diagram of a conventional high voltage switching output driver 10, which is typically formed as part of an integrated circuit (IC) 12. External to the prior art output driver 10 are a pair of bypass capacitors 14 and 16. Prior art high voltage switching output driver 10 includes a pair of low dropout (LDO) regulators labelled LDO1 and LDO2. The output driver 10 also includes a first output driver D1, a second output driver D2, a first power output MOSFET MP1 and a second power output MOSFET MN1. A first input IN1 is coupled to output driver D1 and a second input IN2 is coupled to output driver D2. The two inputs IN2 and IN2 can be differential inputs, or they can be coupled together as single non-differential input.
The high voltage rail 18 for the high voltage switching output driver 10 is at a level PVDD and can be, for example, 20 volts DC (VDC). Ground (PGND) can be at zero VDC, and the outputs of regulators LDO1 and LDO2 can be at 15 VDC and 5 VDC in this example. The drivers D1 and D2 control the MOSFETS MP1 and MN1 to provide the output OUT for driving a load (not shown).
As well known to those of skill in the art, an LDO regulator is a DC linear voltage regulator which can operate with a very small input-output differential voltage. The advantages of a low dropout voltage include a lower minimum operating voltage, higher efficiency operation, and lower heat dissipation. Typically, the main components of an LDO regulator include a power Field Effect Transistor (FET) and a differential (“error”) amplifier. A first input of the differential amplifier is coupled to a stable voltage reference and a second input of the differential amplifier monitors its output. If the output voltage rises too high relative to the reference voltage, the drive to the power FET is adjusted to maintain a constant output voltage.
It should be noted that, in the prior art output driver 10, the drivers D1 and D2 draw significant current from regulators LDO1 and LDO2. The external capacitors 14 and 16, which have values in at least the microfarad range, are required to provide sufficient quantities of current upon demand by the drivers. The need for external capacitors requires that the package for IC 12 have additional pins, which increases the cost and size of the package. Also, the printed circuit board supporting the IC 12 and the capacitors 14 and 16 must be increased in size. Furthermore, the capacitors add additional component and assembly costs to an electronic device.
It will therefore be appreciated that prior art solutions typically require external bootstrap or LDO capacitors (caps) which are costly and which require extra pins on the package of the integrated circuit (IC). It would be advantageous to provide an IC integrating a high voltage switching output driver that does not require external bootstrap components and the attendant extra pins to connect to such external bootstrap components.
These and other limitations of the prior art will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.